Yup..just bring the barges down from Odessa...load em up in a port (say...Sevastopol when it is fixed)...sail on over and unload. I prefer to rail the units up to Rostov and use them to take the city while the umm...other army follows the river line, and crosses it farther along.

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What's the sense of sending $2 million missiles to hit a $10 tent that's empty?

In my Case Blue campaign I have taken the Kuban from Kerch, I dont think I would try it against a human player as it would probably be too risky to get across, but easy enough against the AI.

However, it has been a right slog. There is no room to manoeuvre as most of the hexes impart defensive bonuses to the defender. As it turns out the forces coming down from Rostov ended up helping out the forces coming out of the Kuban. As per LiquidSky above, I reckon the best solution is to use those forces at Rostov and come down South.